I have always assumed that the formulation for the non-toxic vs the toxic version of a bait is identical except for the addition of the active ingredient in the latter. So that in effect unless there is something about the difenacoum/bromadialone or whatever active is present that makes the bait more attractive (seems unlikely) then the toxic version shouldn't be more palatable. Of course that is an assumption based on what would seem sensible but it is possible that the two versions do differ more significantly, for example are there still additives such as bitrex in the non-toxics? Possibly not, and that might alter their palatability (although arguably with bitrex maybe in favour of the non-toxic, but then I've heard of a few animals actually seeming to like the bitter taste!) Nevertheless perhaps there is some other additive or lack of such which causes the animals to either stay away from the non-toxic bait you are using either via neophobic response or a more general repellent effect (the former being more likely)
Two suggestions:
contact the manufacturer and find out exactly what the ingredient difference is.
And/or try a different bait with an alternative non-toxic indicator.

The consultation document did mention it, see table 1 part 3: https://consult.defra.gov.uk/wildlife-management/implementing-aihts-humane-trapping/supporting_documents/AIHTS consultation document FINAL.pdf
I guess if nobody read it and/or didn't bother to respond then it's not surprising that they have been removed. Doubt many people will be concerned that they can't use a Lloyd or a Fenn MKi anymore !!

Brilliant trap, and you are right, it has potential for development. But I think the reason it ended manufacture was it was too well made and too complex compared to many other traps, especially the Fenns, making it expensive. The closest current production trap in terms of concept is the Kania, and it isn't cheap either and has that annoying handle sticking out the side of it. The Fuller was a superb design IMO, perhaps in this new trapping climate there may be a place for a newly manufactured Fuller.

You may be right about the centre baffle and grey squirrel, although perhaps that could be modified. If the aim of the baffle is just to slow down a fast moving stoat so that the strike bar hits it then slowing a grey squirrely down to a complete halt might be fine as its head will be right in the strike zone. And it probably doesn't matter if the trap is used in a single entrance box instead of a run-through tunnel.
I'd agree that the Fenns are more versatile and reasonably priced, however it is also often less efficient at ensuring a quick clean kill, particularly when used sloppily by the inexperienced or disinterested. That isn't to say it can't get a clean kill but I think the point of this trap is to try and ensure that every kill is clean and quick (or as close to that as the legislation is about to demand) and to make it fool proof rather than to rely on the supposed skill (or lack of) that the trapper possesses.
The Tully appears to have passed those tests, it seems unlikely to allow more animals to be caught, just to do so more 'humanely', but until people start using them in the field who really knows if it will do the business

The biggest difference is that as demonstrated in the video this trap can be set easily while held in your hand, a Doc 150 needs to be screwed down to something solid in order to set it effectively. This trap is also designed to share key dimensions with the Fenn trap (same width and height as he says in the vid), That means it should fit into many existing tunnels as most should be longer than this trap anyway. Thus this trap can in theory be used in many of the same situations where people have their Fenns right now as a 'drop in' replacement. The DOC currently has to be used in a box that matches the DOC specifications and has to be attached to it, so it is a much less practical option on both of those scores.
Soon enough the Fenns won't be legal for stoats so replacements will be needed, we should be grateful this guy has gone to the effort to at least try and develop an alternative option, even if it might be imperfect it does seem to offer something different to the DOCs.
Only stoat is covered in these new trap changes coming so there's not much reason for it not to be available for rats, weasels and Squirrels and maybe other things.

The rounded Fenn trap would be the 'Fenn Rabbit trap Mk1'. pretty much the same design as the mkiv and mkvi but with the cross bar forming a semicircle rather than a straight bar. I think they stopped making them because the Mkvi did the same job. Not sure what the benefit of the curved bar was thought to be for rabbits. Maybe so it didn't catch on the tunnel sides so bad, but it think it was slightly taller so that wouldn't add up.

That seems a bit contradictory, maybe we should just clarify the exact position:
Here's a direct quote from section 1(3) of the badgers Act 1992: "A person is guilty of an offence if, except as permitted by or under this Act, he has in his possession or under his control any dead badger or any part of, or anything derived from, a dead badger."
The caveat is the next section 1(4):
"A person is not guilty of an offence under subsection (3) above if he shows that—
.
(a)
the badger had not been killed, or had been killed otherwise than in contravention of the provisions of this Act or of the M1Badgers Act 1973; or
.
(
the badger or other thing in his possession or control had been sold (whether to him or any other person) and, at the time of the purchase, the purchaser had had no reason to believe that the badger had been killed in contravention of any of those provisions.
The Question by the OP is about ensuring he can show he is complying with 1(4)a so he doesn't get prosecuted by some overzealous person under the very real (i.e. it exists) section 1(3)!"
Seems clear, but vague at the same time. i.e. clear that you can possess if you can show that you came about it lawfully, but vague as to how exactly you do that.

I've scoured the internet but can't find any decent images of a Fenn Mk2, I'm interested in how it's different to the MK3. I know it's a bit lighter but not sure if there are any minor differences in shape. Does anyone know where some comparative photos can be found?

"Depends what time in the morning it's tapping the window...anytime before 7:30 is a good reason"
Based on what?
There isn't a general licence that covers that particular problem, Some people might like to make out it's a 'health' issue, but good luck with that should some busybody report you to an unsympathetic PC.....
If the OP want's to make sure he isn't inadvertently breaking any law he should apply to Natural England for a licence, if his action is justified under the general licence they will of course tell him to carry on.
Encouraging people to do things that may be questionable or inhabit legal grey areas (no matter how minor) is ultimately not going to do anyone who shoots any favours. Do it right and do it legal.